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Notes
79RC32438 User Reference Manual
19 - 1
November 4, 2002
Chapter 19
JTAG Boundary Scan
Introduction
The RC32438 is a general-purpose integrated processor that incorporates a high performance CPU
core and a number of on-chip peripherals. There are 2 TAP controllers on the RC32438, one for the CPU
core (referred to as the MIPS32 CPU Core TAP Controller), described in the next chapter (Chapter 20), and
one for System Logic controller, described in this chapter.
The System Logic TAP Controller is used to provide conventional standard JTAG Boundary Scan
access to the RC32438 pin interface. The MIPS32 CPU Core TAP Controller is used to provide access to
the EJTAG interface on the CPU Core.
The two TAP Controllers are connected in parallel as shown in Figure 19.1 and share the JTAG control
pins, except for separate JTAG_TMS and EJTAG_TMS pins. Thus at least one of the two TAP Controllers
must be in Test-Logic-Reset at any given time, so that the JTAG_TDO pin is only actively being driven from
no more than one of the TAP Controllers. For example, if neither TAP Controller is in use, they both can be
reset by asserting JTAG_TRST_N, or by asserting both jtag_tms and ejtag_tms high for 5 consecutive
JTAG_TCKS clocks. If the MIPS32 CPU Core TAP Controller is to be used, then the System Controller TAP
Controller must be reset by asserting jtag_tms high for 5 consecutive JTAG_TCK clocks. If the System
Controller TAP Controller is to be used, then the MIPS32 CPU Core TAP Controller must be reset by
asserting EJTAG_TMS high for 5 consecutive JTAG_TCK clocks.
The MIPS32 CPU Core TAP Controller is used primarily for EJTAG support, since many EJTAG func-
tions are accessed via the MIPS32 CPU Core TAP Controller JTAG port.
Note that the Boundary Scan
Register for the internal CPU Core is not used, as it would access internally connected CPU Core
ports/pins.
Instead the System Controller TAP Controller Boundary Scan Register is provided for RC32438
conventional JTAG pin access, control, and boundary scan.
Figure 19.1 Dual TAP Controller Block Diagram
Boundary Scan Cells
System Controller
TAP
CPU Core
TAP
EJTAG
JTAG_TCK, JTAG_TDI,
JTAG_TRST_N
JTAG_TMS
EJTAG_TMS
JTAG_TDO
Boundary Scan Cells
B
B